1. Field of the Invention
The present invention relates to a switching system and a method of controlling a line concentrator provided in the switching system to connect lines, and more particularly relates to a switching system and a method of controlling a line concentrator provided in the switching system to connect to other line concentrators.
2. Description of the Related Art
Recently, with the rapid spread of Internet usage, the number of Internet service providers (ISP) that provide services to connect to the Internet, as well as the number of subscribers who use the Internet through dial-up ISP connections, has increased sharply. Additionally, introduction of a flat rate to Internet services has been considered, and thus it is predictable that a percentage of occupation of lines for a long period by ISP-connection subscribers will increase further in the future. Each corporation has been researching and developing a new network that allows Internet users to connect to the Internet constantly. However, it is predicted that it takes time to replace the existing network with the new network completely, and the investment in equipment for each ISP with introduction of the new network is enormous. Under such circumstances, each ISP needs to cope with the rapid spread of the Internet use by using the existing network effectively as well as constructing the new network.
A description will now be given of a network using a conventional switching system with reference to FIG. 1. In FIG. 1, a line-concentrating unit 12 is connected to a switching unit 10. Additionally, a remote line-concentrating unit 16 is connected to the switching unit 10 through trunks 13 and 14. Subscribers A and B are connected to the line-concentrating unit 12. An ISP network 20 is also connected to the line-concentrating unit 12 through a PRI (Primary Rate Interface) 15 of an ISDN (Integrated Services Digital Network) line. Subscribers C and D are connected to the remote line-concentrating unit 16. A subscriber E is connected to the switching unit 10. A switching unit 30 is connected to the switching unit 10 through trunks 17 and 18. A line-concentrating unit 32 is connected to the switching unit 30. In addition, a remote line-concentrating unit 36 is connected to the switching unit 30 through trunks 33 and 34. Subscribers F and G are connected to the line-concentrating unit 32. Subscribers H and I are connected to the remote line-concentrating unit 36. Additionally, a subscriber J is connected to the switching unit 30.
In a case that the subscribers A and C located under the switching unit 10 attempt to connect to the ISP network 20 by a dial-up connection, the subscribers A and C are connected through the PRI 15 to the ISP network 20. To be concrete, in a case that an ISP-connection subscriber such as the subscriber A and the PRI 15 that is connected to the ISP network 20 are located under the line-concentrating unit 12, the subscriber A connects to the PRI 15 via only the line-concentrating unit 12 not through the switching unit 10 when the subscriber A has captured the PRI 15 under the line-concentrating unit 12. Such a method to connect to the PRI 15 simply through the line-concentrating unit 12 by the subscriber A is called an off-road function of a line-concentrating unit.
However, other ISP-connection subscribers such as the subscribers F and H located under the switching unit 30 also connect to the ISP network 20, and they call the switching unit 10 through trunks 17 and 18, and are connected to the ISP network 20 via the PRI 15 located under the switching unit 10. If a large number of the ISP-connection subscribers occupy the lines by use of dial-up connections for a long period as described above, the lines are overcrowded at overcrowded points A through F, and thus general subscribers such as subscribers B, D, E, G, I and J cannot capture the lines for regular calls. The first method to solve the above-described problem is to increase the number of switches in the switching unit 10 and the number of trunks located between the switching units 10 and 30 by a common carrier considering the occupation time of the lines by the dial-up ISP connections. The second method is to provide a new ISP access point 37 indicated by a broken line by an Internet service provider and to provide a PRI 38 that is indicated by a broken line and is connected to the ISP access point 37 under the line-concentrating unit 32 by the common carrier.
However, in the first method, a large number of inefficiently used extension equipment such as the trunks and the switches must be added to the switching units 10 and 30 so as to correspond to long-period calls concentrated in a specific time of a day. Such a method does not follow a design concept of a conventional switching system that minimizes the investment in equipment such as the trunks and the switches by sharing the equipment of the switching system among calls on the assumption that most of the calls are short-period calls. Additionally, the first method includes a problem that it is not simple to maintain and manage the entire network shown in FIG. 1 for providing sufficient services to each of the ISP-connection subscribers and the general subscribers since the equipment such as the trunks and the switches of the switching units 10 and 30 are shared among the long-period calls that are not considered in the conventional switching system and the short-period calls. In the second method, the Internet service provider must extend the ISP network 20 to a remote location for preparing the new ISP access point 37, and thus additional investment in equipment used for extending the ISP network 20 is necessary. In addition, a dial number for accessing each line-concentrating unit must be changed for a subscriber located under a line-concentrating unit to capture a PRI under the line-concentrating unit when accessing the ISP network 20.